The conventional method of manufacturing superconducting wires includes one or more steps of hot extruding composite billets followed by drawing and wire drawing down to the final diameter. These billets are generally constituted by a cylindrical body which, depending on circumstances, contains several hundred to several tens of thousands of components which are in the form of rods and which may themselves be composite.
One possible way of reducing the manufacturing costs would be to reduce the number of extrusion steps, and that would simultaneously improve the performance of the superconducting strand. Such a reduction in the number of steps would be possible if it were possible to manufacture billets including a large number of rods. However, there are practical difficulties in making up such billets, and these difficulties increase with the number of components:
with rods of hexagonal section as are normally used to ensure good packing, the time required for stacking the rods is long even if they are properly smooth and not twisted; the number of hexagonal rods that can be assembled together properly without special tooling remains very low; and PA1 the use of rods that are circular in section reduces stacking time but leads to a poor packing factor which is due to the numerous cross-overs between the rods and to the existence of empty spaces between them.